This application claims the benefit priority of Taiwan application serial No. 89125445, filed Nov. 30, 2001.
1. Field of the Invention
The invention relates to a quad flat non-leaded package. More particularly, the invention relates to the bonding structure of a quad flat non-leaded package.
2. Description of the Related Art
As the era of information technology progresses, the transmission and processing of information and documents are increasingly performed via sophisticated electronic products. Accompanying the progress of technology, many commercial products with more convenient features have been promoted, such as mobile phones, computers, audio-video articles, etc. In such a context, various high-density packaging structures thus are manufactured, such as chip scale packages (CSP), multi-chip modules (MCM), etc.
Among these various packaging structures, the quad flat non-leaded package (QFN) has been developed by the Matsusita company. The quad flat non-leaded package (QFN) usually is a leadframe-based chip scale package (CSP). Advantageously, the conductor traces of the non-leaded chip scale package (CSP) are short, which reduces the deterioration of the transmitted signal. Such a packaging structure is conventionally used to package low pin count semiconductor elements.
FIG. 1 shows a conventional quad flat non-leaded package (QFN) structure. The conventional quad flat non-leaded package 100 comprises a chip 110, a leadframe 130, and a molding compound 160. The chip 110 has an active surface 112 and a corresponding back surface 114, wherein the active surface 112 of the chip 110 comprises a plurality of bonding pads 116. The leadframe 130 comprises a die pad 140 and a plurality of leads 150, wherein the die pad 140 has an upper surface 142 and a corresponding lower surface 144, and each of the leads also has an upper surface 152 and a corresponding lower surface 154. Within the package structure, the chip 110 is adhered by the back surface 114 thereof to the upper surface 142 of the die pad 140 and, through the bonding wires 170, the bonding pads 116 are respectively connected to the leads 150. The molding compound 160 encapsulates the chip 110, the bonding wires 170, the upper surfaces 152 of the leads 150, and the upper surface 142 of die pad 140 while exposing the lower surfaces 154 of the leads 150 and the lower surface 144 of the die pad 140.
The quad flat non-leaded package (QFN) 100 is further mounted upon a printed circuit board 180 that has a plurality of contact nodes 182 and a ground contact node 184 located at the center of the contact nodes 182. Via a reflow process, bonding materials 192 and 194 respectively connect the lower surface 154 of the leads 150 to the contact nodes 182 and the lower surface 144 of the die pad 140 to the ground contact node 184 of the printed circuit board 180.
FIG. 1A shows an upward view of the quad flat non-leaded package of FIG. 1 in which the die pad and the leads are exposed through the molding compound. In the conventional quad flat non-leaded package (QFN) 100, the lower surface 144 of the die pad 140 is square-shaped and is substantially large. As a result, when the bonding material 194 underneath the die pad 140 is reflowed, the generated surface tension on the bonding material 194 causes the die pad 140 to drift above the ground contact node 184. The deviation of the position of the die pad may cause an inaccurate connection of the leads 150 to the contact nodes 182 of the printed circuit board 180 and therefore decrease the quality of the electrical connections.
An aspect of the invention is to provide a quad flat non-leaded package and a leadframe structure for a quad flat non-leaded package in which the quality of the electrical bonding between the quad flat non-leaded package (QFN) and the printed circuit board is improved.
Another aspect of the invention is to provide a quad flat non-leaded package and a leadframe structure for a quad flat non-leaded package wherein the leads of the quad flat non-leaded package (QFN) can be accurately connected to the contact nodes of the printed circuit board.
To attain the foregoing and other objectives, the present invention provides a quad flat non-leaded package (QFN) that, according to a preferred embodiment, comprises: a die pad having a first upper surface and a corresponding first lower surface, wherein the first lower surface of the die pad has a plurality of interlacing slots, each of the interlacing slots uniformly extending to the edges of the lower surface of the die pad to define a plurality of island-like blocks; a plurality of leads disposed at the periphery of the die pad, wherein each of the leads respectively has a second upper surface and a corresponding second lower surface substantially coplanar with the surface of the island-like blocks; a chip having an active surface with a plurality of bonding pads thereon respectively connected to the leads and a corresponding back surface adhered onto the first upper surface of the die pad; and a molding compound encapsulating the chip, the second upper surfaces of the leads, and the first upper surface of the die pad while exposing the surface of the island-like blocks and the second lower surfaces of the leads.
To attain the above and other objectives, the invention further provides a quad flat non-leaded package (QFN) suitable to be arranged on a printed circuit board, the printed circuit board comprising a plurality of contact nodes and a ground contact node disposed at the center of the contact nodes. The quad flat non-leaded package (QFN) suitable to be arranged on the printed circuit board, according to another embodiment of the present invention, comprises: a die pad having a first upper surface and a corresponding first lower surface, wherein the first lower surface of the die pad has a plurality of interlacing slots, each of the interlacing slots respectively extending to the edges of the lower surface of the die pad, thereby forming a plurality of island-like blocks; a plurality of leads disposed at the periphery of the die pad, wherein each of the leads respectively has a second upper surface and a corresponding second lower surface substantially coplanar with the surface of the island-like blocks; a chip having an active surface with a plurality of bonding pads thereon respectively connected to the leads and a corresponding back surface adhered onto the first upper surface of the die pad; and a molding compound encapsulating the chip, the second upper surface of the plurality of leads, and the first upper surface of the die pad while exposing the surface of the island-like blocks and the second lower surfaces of the leads. The second lower surface of each of the leads is respectively connected to the contact nodes of the printed circuit board through a plurality first bonding materials, while the islands-like blocks are respectively connected to the ground contact node through a plurality of second bonding materials to provide electric and heat dissipation paths.
To attain the above and other objectives, the invention further provides a leadframe suitable for use in a quad flat non-leaded package (QFN). The leadframe, according to another embodiment of the present invention, comprises: a die pad having a first upper surface and a corresponding first lower surface, wherein the first lower surface of the die pad has a plurality of interlacing slots, each of the interlacing slots extending uniformly to the edges of the lower surface of the die pad to form a plurality of island-like blocks; and a plurality of leads disposed at the periphery of the die pad, wherein each of the leads respectively has a second upper surface and a corresponding second lower surface substantially coplanar to the surface of the island-like blocks.
In an example of the present invention, the die pad is substantially square and the island-like blocks are arranged in a matrix with the slots respectively parallel to an edge of the die pad. In another example of the present invention, the island-like blocks can be arranged in a matrix with the slots respectively secant at an angle to an edge of the die pad. The surface of the island-like blocks can be rounded.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.